United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/041 Mar. 1987
Project Summary
Pilot Demonstration of the
Air Curtain System for
Fugitive Particle Control
R. Lockwood Williams and Michael Duncan
Fugitive emissions are the major
source of uncontrolled emissions for
many industrial plants. There are pres-
ently no high performance, inexpensive
control techniques available for many
fugitive sources. The present technology
is not only expensive, it is often mar-
ginally effective and typically consists
of hooding at the source, or total build-
ing enclosure and evacuation.
A simpler and less expensive method
is to divert the emissions with an air
curtain (and fans in some cases) into a
control device located near the source.
This greatly reduces processing of un-
contaminated air. The technical and
economic feasibility of using an air cur-
tain transport system for controlling
buoyant fugitive particle emissions from
mold pouring operations was demon-
strated at a Naval foundry in California.
The pilot plant system used a hori-
zontal air curtain to capture and convey
the buoyant fugitive particle emissions
to a particle collection filter unit. High
Efficiency Paniculate Air (HEPA) filters
in the filter unit collected the particles
with the aid of suction fans. Results
from the pilot plant tests indicate that
the air curtain capture efficiency, the
measure of the air curtain's ability to
capture and convey the fugitive emis-
sion plume, is between 63 and 105%,
depending on air curtain slot exit velo-
city, and subject to a ±18% error limit.
Results also indicate that collection ef-
ficiency of the HEPA filters for the
particle size range of the mold emissions
is 99%. The overall capture and con-
tainment efficiency of the pilot plant,
when operating in the appropriate slot
velocity range, can be expected to be
between 90 and 99% when considered
as a package.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering In-
formation at back).
Introduction
Fugitive emissions are air pollution
emissions which have not passed through
a stack or duct. They are diffuse, and
typically come from many small sources
rather than from a single large source.
Fugitive particle emissions tend to be site-
specific: open operations, storage and
disposal of materials and wastes, in-
completely controlled point sources, and
poor housekeeping all provide maximum
potential for their release.
One method for controlling buoyant
fugitive emissions is to gather and convey
them to conventional air pollution control
devices. Typical systems of this type in-
volve hooding at the local source of emis-
sions, or total building enclosure and
evacuation. These systems often require
high capitol and energy costs, especially
when there are many small, diffuse
sources.
A simpler and less expensive method is
to divert the emissions with air curtains
(and fans in some cases) into a control
device located near the source. This great-
ly reduces the processing of uncon-
taminated air. An air curtain is a wedge-
shaped flow field of air that is formed by
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blowing air through a slot. A major ad-
vantage of air curtains over hoods is that,
for a given volumetric flow rate, an air
curtain can cause air movement at a
much greater distance than hoods (about
30 times greater). Another advantage is
that air curtains allow free movement of
equipment and personnel in the area to be
controlled.
Extensive tests were conducted to deter-
mine the technical and economic feasi-
bility of using an air current transport
system for controlling buoyant fugitive
particle emissions from mold pouring
operations at a Naval foundry in San
Diego, CA.
Objectives
The principal objective of this contract
was to demonstrate the technical and
economic feasibility of the use of an air
curtain system at an industrial site.
The itemized objectives for this study
were:
1. Select a pilot plant demonstration
site with a suitable industrial
participant.
2. Conduct a series of operational
design verification tests of the emis-
sion control system.
3. Demonstrate the pilot plant at the
selected industrial site in order to
compile an extensive performance
characterization of the emission
control system.
4. Produce a detailed evaluation of the
emission control system.
Pilot Plant
Description
Pilot plant demonstration sites were
investigated to determine an appropriate
location with a significant source of fugi-
tive emissions. After extensive investiga-
tion, a Naval maintenance foundry in San
Diego, CA, was selected.
The SCAT scrubber developed under a
previous EPA contract used air curtains
and/or push jets to contain, divert, and
convey the fugitive emissions of an in-
dustrial process into a charged spray
scrubber. This scrubber would have used
a low pressure drop entrainment sep-
arator to trap the spray drops and the
collected particles for subsequent dis-
posal. Investigations into the emissions
to be controlled indicated, however, that
the charged spray scrubber would not be
applicable for two reasons: the particles
were too small (0.2 to 0.4 jimA diameter),
and the Navy did not want a wet system.
It was determined that the appropriate
particle collection device should rather
be a filtration unit which would still
operate in conjunction with air curtains
and/or push jets to contain, divert, and
convey the fugitive emission of the in-
dustrial process.
A complete pilot plant-fugitive emission
control system was evaluated. The high
velocity air curtain airstreams entrain the
fugitive particle emissions from foundry
molds (plus some additional air), and carry
them away from the source. At a con-
venient distance downstream, the particle
laden airstream is pulled into a filter unit,
and the emission particles are removed.
The cleaned gases are then exhausted
into the atmosphere by the fans used to
pull the air through the filter unit.
The pilot plant consisted of an air cur-
tain and a filter bank system as shown in
Figure 1. The single slot air curtain was
horizontal and adjustable in height and
angle of air outlet orientation. The size
and strength of the air curtain were deter-
mined by design verification tests.
The filter unit consisted of an array of
High Efficiency Paniculate Air (HEPA)
filters (series 95) and suction fans with
volume dampers to move the emission
laden air through the unit. The filter bank
was also adjustable in height.
The units are arranged so that the air
curtain sweeps air across the top of the
fugitive emission source, traps and con-
veys the emissions, and delivers them to
the filter unit for cleanup.
Pilot Plant Test Methods
Overall effectiveness of the pilot plant
depends on both the ability of the air
curtain to capture and convey the fugitive
particles and the ability of the filter to
collect them. Consequently, two tests
were used to evaluate pilot plant opera-<
tion: air curtain capture efficiency and"
filter collection efficiency.
Air Curtain Capture
Efficiency Tests
To determine air curtain capture ef-
ficiency, which is the measure of the
ability of the air curtain to capture the
plume of a foundry mold, the mold emis-
sion rate and the portion of this emission
captured by the air curtain need to be
known. Mold emission rate varies widely
from mold to mold, and cannot be mea-
sured while the pilot plant is operating.
Thus, the emitted particles cannot be
used to determine capture efficiency.
Particles emitted from the molds are
small, and behave similar to a gas. There-
fore, the air curtain capture efficiency
was determined with sulfur hexafluoride
(SF6) tracer gas. SF6 is chemically and
physiologically inert, nonflammable, and
noncorrosive with a viscosity that is
approximately the same as that of air.
The SF6 was metered directly into the
buoyant mold plume after a metal pour.
The air curtain air stream conveys both
the mold emissions and the SF6 to the
filter unit. Traverse gas samples were
obtained at the outlet of the filter unit tc
determine the concentrations of tracer
gas in the outlet streams. The ratio of SF,
outlet mass flow rate to total SF6 injectior
was used to determine the capture ef-
ficiency. Gas flow rate was determinec
with a standard pitot tube transverse o'
the duct. This was done to determine the
overall flow rate of the unit and is requirec
in order to assist in the determination o
the SF6 concentrations.
Fan
Exhaust
Air
Curtain
Duct
_d ,._B .
Mold
O O
Particle
Control
Device
Figure 1. Pilot plant arrangement.
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Bitter Collection
Efficiency Tests
To measure the collection efficiency of
the filters used in the pilot plant unit, the
particle concentrations in both the inlet
and outlet airstreams of the pilot plant
unit needed to be measured simulta-
neously. Because of dilution by the air
curtain, particle concentrations at the
inlet and outlet of the pilot plant filter unit
were found to be too low to allow mea-
surement with cascade impactors. Con-
sequently, a small scale unit was built to
duplicate the pilot plant unit, incorporating
the same filters and filter surface
velocities while minimizing dilution of
the mold emissions. This small scale unit
consisted of a hood to place over the
emission source, ducting, and a small
version of the same HEPA filter material.
A blower conveyed the mold emissions
through the system while particles were
sampled both up- and downstream of the
filter.
Particle size distributions and concen-
trations were measured with both cascade
impactors and an electrical aerosol size
analyzer. Cascade impactors were used
to obtain data on the larger particles
(greater than 0.5 ^mA) of the mold plume,
and the electrical aerosol size analyzer
was used for the smaller particles (less
than 0.5 /urnA). Fractional efficiency was
calculated from the measured size distri-
butions and concentrations.
Results
Air Curtain Capture Efficiency
Results from the pilot plant tests
indicate that the air curtain capture ef-
ficiency is between 63 and 105%, de-
pending on the air curtain slot exit velocity
of between 8.40 m/s (1653 ft/min) to
13.53 m/s (2662 ft/min). This capture
efficiency is subject to a ± 18% error
limit. The capture efficiency increases
with increasing air curtain exit slot velo-
city. For the pilot plant arrangement at
the demonstration site, the slot velocity
for 100% capture of the mold plume is in
the range of 12.19 to 13.72 m/s (2400 to
2700 ft/min). This information can be
seen in Figure 2.
Filter Collection Efficiency
Results of cascade impactor sampling
are shown in Figure 3. Penetration scat-
ters from 0.01 to above 50%. The scat-
tering of data points is caused by low
mass gain of each impactor substrate.
/lost of the weight gains of the substrates
were in the range of 0.1 mg which,
unfortunately, is within the error range of
the electronic balance being used to
weigh them.
Results of electrical aerosol size
analyzer sampling are shown in Figure 4.
The measured penetration is less than
1% for particles between 0.1 and 0.4
jumA diameter, which is better than the
5% rating at 0.3 /urn of the HEPA series
95 filters.
Conclusions
The pilot plant installed at the demon-
stration foundry site, consisting of an air
curtain transport system and a HEPA
filter bank with suction fans, constituted
an efficient, economical, and versatile
system for the control and entrapment of
buoyant fugitive particle emissions from
foundry molds. The overall capture and
containment efficiency of the pilot plant
is between 90 and 99%. It is highly
probable that the type of system quantified
here will find widespread utility in many
other industrial applications related to
fugitive particle emission control.
The quality control evaluation in the
full report discusses data accuracy deter-
minations and applicability limitations.
740
130
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X n| i\C\S.
R. L. Williams and M. Duncan are with Air Pollution Technology, Inc., San Diego,
CA 92109.
Dale L. Harmon is the EPA Project Officer (see below).
The complete report, entitled "Pilot Demonstration of the Air Curtain System for
Fugitive Particle Control," (Order No. PB 87-132 817/AS; Cost: $18.95. subject
to change} will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-86/041
0000329 PS
U S ENVIR PROECTION AGiSCY
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